<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #app {
            width: 100px;
            height: 100px;
            margin: 100px;
            padding: 200px;
            border: 1px solid black;
            box-sizing:border-box
        }
    </style>
</head>

<body>
    <div id="app"></div>
</body>

</html>